A valve unit of the aforementioned type may be a pressure control valve an antilock brake system in a vehicle, in which two main valves arranged in the main housing, that is to say an inlet valve and an outlet valve, are embodied as diaphragm valves with diaphragms arranged largely in the plane of division, and in which the pilot valves assigned to these and arranged in the housing cover are embodied as 3/2-way directional control solenoid valves. The vehicle may be a motor vehicle or a rail vehicle.
A pressure control valve of an antilock brake system has the three switching functions: “pressure build-up”, “pressurization” and “pressure reduction”. In the “pressure build-up” switching function of the valve unit the inlet valve is opened and the outlet valve is closed, so that the brake pressure generated by way of a brake valve on the brake pressure inlet is relayed in full by the pressure control valve to the brake pressure outlet and to at least one wheel brake cylinder connected thereto.
Since the “pressure build-up” switching function corresponds to the rest state of the valve unit, the pilot valve of the inlet valve with its solenoid in the unenergized state connects the control chamber of the inlet valve to a control line carrying the low control pressure. In exactly the same way the pilot valve of the outlet valve with its solenoid in the unenergized state connects the control chamber of the outlet valve to a control line carrying the high control pressure. In the “pressurization” switching function of the pressure control valve the inlet valve and the outlet valve are closed, so that the brake pressure prevailing on the brake pressure outlet and at least the one wheel brake cylinder connected thereto can then be kept constant. For setting this switching function, only the pilot valve of the inlet valve is switched over by energizing its solenoid, thereby admitting the high control pressure to the control chamber of the inlet valve. In the “pressure reduction” switching function of the pressure control valve the inlet valve is closed and the outlet valve is opened, so that the brake pressure outlet and at least the one wheel brake cylinder connected thereto are then vented. For setting this switching function, both pilot valves are switched over by energizing their solenoids, thereby admitting the high control pressure to the control chamber of the inlet valve and the low control pressure (ambient pressure) to the control chamber of the outlet valve.
The “pressurization” and “pressure reduction” switching functions of the pressure control valve are antilock brake functions, which are intended to prevent locking of at least the one assigned wheel during braking. These switching functions are controlled through a corresponding activation of the pilot valves by a control module of the antilock brake system, in which the signals from wheel brake sensors are evaluated in order to detect any imminent or incipient locking of the braked wheels.
Such a valve unit is described, for example, in DE 25 17 571 A1. In this known valve unit an elongated valve housing is subdivided by a plane of division, horizontal in the fitted position, into a housing lower part and a housing upper part. The brake pressure inlet and the venting outlet are arranged, horizontally oriented, largely axially opposite in a longitudinal direction and the brake pressure outlet is arranged, likewise horizontally oriented, largely centrally at right angles thereto in the housing lower part. The diaphragm valves are arranged in series, in the longitudinal direction of the valve housing, in the housing lower part between the brake pressure inlet and the venting outlet, with parallel actuation axes and an arrangement of the diaphragms in a common diaphragm plane, largely corresponding to the plane of division, clamped between the housing lower part and the housing upper part. The pilot valve of the inlet valve and the pilot valve of the outlet valve are arranged, each with their actuation axis oriented vertically and identical switching directions, above the respectively assigned diaphragm valve radially adjacent to one another in the housing upper part.
In a further such valve unit disclosed in EP 0 498 584 B1 the valve housing is subdivided by a plane of division, vertical in the fitted position, into an inlet housing and an outlet housing. The brake pressure inlet is arranged horizontally oriented in the top of the inlet housing. The brake pressure outlet is arranged horizontally oriented in the outlet housing largely axially opposite the brake pressure inlet, whereas the venting outlet is arranged, directed vertically downwards, in the outlet housing. The diaphragm valves are arranged one vertically above the other in the outlet housing between the brake pressure outlet and the venting outlet with parallel actuation axes and an arrangement of the diaphragms in a common diaphragm plane, largely corresponding to the plane of division, clamped between the outlet housing and the inlet housing. The pilot valve of the inlet valve and the pilot valve of the outlet valve are arranged radially adjacent to one another in the inlet housing, each with their actuation axes horizontally oriented and opposed switching directions, approximately centrally at right angles to the compressed air inlets and compressed air outlets and parallel to the plane of division. The solenoids of the pilot valves are arranged in a solenoid block, which is arranged together with the inserted mechanical components of the solenoid valves between a housing upper part and a housing lower part of the inlet housing. For sealing purposes, seals or sealing rings are arranged between the solenoid block, the valve blocks, and the valve seats of the solenoid valves on the one hand, and the housing upper part and the housing lower part of the inlet housing on the other. For fixing the housing upper part and the housing lower part to the solenoid block of the solenoid valves on the one hand, and for clamping the diaphragms of the diaphragm valves on the other, the housing upper part and the housing lower part of the inlet housing are each bolted to the outlet housing.
Finally, DE 10 2008 028 439 B3 describes such a valve unit, in which an elongated valve housing is subdivided by planes of division, largely horizontal in the fitted position, into a housing lower part, a housing upper part and an intermediate plate arranged between them. The brake pressure inlet, the brake pressure outlet and the venting outlet are arranged, each horizontally oriented, in the housing lower part. The diaphragm valves are arranged in series in a longitudinal direction in the housing lower part, with parallel actuation axes and an arrangement of the diaphragms in a common diaphragm plane, largely corresponding to the plane of division between the housing lower part and the intermediate plate, clamped between the housing lower part and the intermediate plate. The pilot valve of the inlet valve and the pilot valve of the outlet valve are arranged radially adjacent to one another in the housing upper part, each with their actuation axes oriented vertically and identical switching directions, approximately centrally above the diaphragm valves. The intermediate plate is bolted to the housing lower part. The housing upper part is bolted via an outer cover to the intermediate plate or to the housing lower part. Seals are arranged in the plane of division between the housing upper part and the intermediate plate.
A valve unit of the aforementioned type may also be a relay valve, however, in which a main valve arranged in the main housing are embodied as a piston valve having a piston displaceably supported in the actuation axis and a spring-loaded double-acting valve that can be actuated by the former, and in which the assigned pilot valve, arranged in the housing cover, is embodied as a 3/2-way directional control solenoid valve. The function of a relay valve, given the high brake cylinder volumes of the wheel brake cylinders connected to the brake pressure outlet, is to reduce the response time in braking operations and also when releasing the brakes, that is to say to bring about a rapid ventilation and venting of the connected wheel brake cylinders.
The valve unit of the type here under consideration comprises two interconnected main components, that is to say the main housing having the compressed air connections and containing at least the one main valve, and the housing cover containing at least one pilot valve. The main housing is for the most part manufactured as a die-cast light-alloy component. The housing cover is usually composed of a plastic, which serves for overmolding an insert containing at least the one pilot valve, for example. The housing cover is normally connected to the main housing by means of a bolted flange connection, in which bolts inserted into flange holes in the housing cover are bolted to threaded holes in the main housing. Due to the stresses imposed by the control pressures prevailing in the control chamber of the main valve, however, a bolted flange connection requires a relatively large number of bolts. Added to this is the fact that owing to the flow properties of the plastic the flange holes in the housing cover need to be reinforced with metal sleeves, in order to prevent damage to the housing cover. Using M6 bolts, a flange hole diameter of 6.5 mm and a metal sleeve wall thickness of 1.5 mm, this disadvantageously results, with two opposing bolts, in an additional width of the housing cover of 19 mm, even before taking into account the dimensions of the bolt heads.